High frequency energy interchange apparatus



N 1960 w. A. HARMAN HIGH FREQUENCY ENERGY INTERCHANGE APPARATUS 3Sheets-Sheet 1 Filed May 6, 1958 WAPD A. HARMAN INVENTOR.

Nov. 29, 1960 w. A. HARMAN 2,962,620

HIGH FREQUENCY ENERGY INTERCHANGE APPARATUS Filed iviay 6, 1958 5SheetsSheet 2 WAPD A. HAEMAN INVENTOR.

in I {"21 BY Nov. 29, 1960 w. A. HARMAN HIGH FREQUENCY ENERGYINTERCHANGE APPARATUS 3 Sheets-Sheet 5 Filed May 6, 1958 WARD A. HARMANINVENTOR.

Anon/5 HIGH FREQUENCY ENERGY INTERCHANGE APPARATUS Ward A. Harman, PaloAlto, Calif., assignor to General Electric Company, a corporation of NewYork Filed May 6, 1958, Ser. No. 733,328

20 Claims. (Cl. 315-35) This invention relates to the class of deviceswhich depend upon an interchange of energy between a stream of electronsand a radio frequency field to provide amplification and/oroscillations. More particularly, the invention relation to the class ofhigh frequency energy interchange devices known as traveling wave tubeswhich include an electron gun for producing a stream of electrons in aninteraction region and a radio frequency circuit or transmission linefor producing radio frequency fields in the region of interaction, andthe invention has for one of its principal objects the provision ofimproved methods and means for transferring high frequency energybetween the radio frequency circuit and a wave guide or transmissionline or the like and collecting electrons from the electron stream.

' A major concern when utilizing generators or power sources is toobtain a maximum of power transfer from the generator to the desiredload device. In other words, it is desirable to make the best use ofpower generated by the source. This is none the less true for generatorsand amplifiers in the microwave frequency spectrum such as travelingwave tubes. The means of obtaining maximum power transfer between atraveling wave energy interchange device and its load must be dilierentfrom the means used in most devices which operate in lower frequencyspectra, because a special type of transmission line, the slow wavetransmission line, is used to obtain amplification and oscillations inthe traveling wave device. Since the slow wave transmission line is acrucial element in the traveling wave tube, the physical designdimensions of the slow wave structure take precedence over otherconsiderations such as the characteristics of the load and transmissionline external to the traveling wave device. In its most common form, theslow wave circuit in a traveling wave tube is a helix which is made ofconductive material.

It is generally not practical to extend the slow wave transmission lineutilized in the traveling wave tube out through the envelope to the loaddevice. As a consequence, the energy must be brought out of thetraveling wave tube and delivered to the load device by moreconventional fast wave transmission line means; for example, a coaxialtransmission line or hollow wave guide. If there is a discontinuitybetween the internal slow wave transmission line and the external fastwave transmission line, that is, if the impedance of one transmissionline is appreciably different from the other transmission line at thejunction between the two, backward traveling waves appear within thetraveling wave tube due to reflections at the discontinuity. Suchreflections interfere with operation of the traveling wave tube. Forexample, such reflections may cause power loss, loss of efiiciencyand/or regeneration.

The problem of matching a slow wave helical transmission line to a fastwave transmission line, such as coaxial cable, is one of providing animpedance match between a transmission line having an impedance on theorder of 300 to 400 ohms (the slow wave line) to a transmission "iceline having an impedance on the order of ohms (fast wave line). Thematching problem is not difficult for a particular frequency or alimited frequency range but the traveling wave tube is generallydesigned to operate over a broad range of frequencies and it isdifiicult to obtain such an impedance match which is effective over thedesired frequency range (e.g., 60 to 300 megacycles per. second).Theparticular problem is not a new one and the match is generallyaccomplished by a means known as tapering the impedance. That is, theimpedance 300 to 400 ohms is gradually tapered down or reduced over alength of the slow wave transmission line which is sufficiently long tominimize reflections in the frequency range of interest. Whenconsidering any individual frequency, such a match represents anengineering compromise.

The impedance taper, when considered in connection with the outputtransmission line, must be accomplished in the region of the outputportion of the device. However, the portion of the slow wave circuitassociated with the impedance taper is only partially effective forinter action with the stream and thus only partially effective inproducing gainor amplification. Thus, interaction is only partiallyeffective in the region where the electron stream,

is most effective in producing a transfer of energy. In view of thisfact, impedance tapering is ideally done in a region beyond thatoccupied by the electron stream because such an arrangement allows theshortest possible length .of electron stream for a given amplificationor gain.

It is important to keep the electron stream as short as possible sincethe stream is typically focussed by a mag{ netic field supplied by afocussing solenoid or magnet. In either case, the focussing fieldproducing apparatus is heavy and cumbersome. extra power supply isrequired. If the length of the electron stream is kept to a minimum, thesize and weight of the focussing equipment can be kept to a minimum.There is the possibility of reducing the stream length from either endof the device; however, the electron gun and collector generally can notbe placed within the region of outside the region occupied by theelectron stream.

Accordingly, an object of the present invention is to provide acollector in a traveling wave tube of such a shape which will allow itto perform as a tapered impedance matching section as well as acollector for the electron stream and provide for a large percentage ofthe impedance tapering to be done beyond the point where the electronstream is collected.

It should be noted that the problem of physical length is most acutewith extremely low frequency traveling wave devices, e.g., travelingwave tubes which operate in the frequency spectrum between 60 and 300megacycles. The low frequency traveling wave tube cannot simply bescaled from higher frequency models. With a direct scaling of higherfrequency models, the indication would be that a typical Watt 60megacycle tube might be 20 or 30 feet in length. Such a tube is notpractical and the tube dimensions must be reduced by arranging thevarious tube elements in such a way that the required power and gain canbe obtained in a length of not over 2 to 3 feet. Since the length ofstructure required to obtain a broad band tapered impedance match isdirectly related to wave length, in low frequency tubes the input andout-- put matches, which generally require a minimum of near- When asolenoid is used, an

typical half wave length of a helical slow wave transmission line at 60megacycles is approximately 4 inches. If the tube is on the order of 24inches long, the matching length represents about 30% of tube lengthat-this frequency. If the tapering portion of the slow wave circuit is'done prior to collection of the electron stream, and the portion of theslow wave circuit in the impedance match area is substantiallyineffective in providing interaction between the electron stream and theradio frequency waves, then the additional half a circuit wave lengthmay be considered substantially wasted and the electron stream and tubeare required to be at least half a circuit wave length longer.

Accordingly it is another object of this invention to provide means forreducing the length of the high frequency energy interchange device to aminimum, which means includes means for simultaneously matching theimpedance of a slow wave transmission line to a fast wave transmissionline and a means for collecting electrons from the electron stream.

In carrying out the present invention, a tapered impedance matchingsection is provided between the slow wave transmission line of atraveling wave energy interchange. device and a fast wave outputtransmission line which output tapered impedance match is accomplishedby providing an electron collector and impedance match along the outputend of the slow wave transmission line. The physical size and positionof the match-collector are arranged in such a manner that electrons fromthe stream are collected near the beginning of the impedance taper.

The novel features which are believed to be characteristic of thisinvention are specifically set forth in the appended claims. Theinvention itself, however, both as to its organization and method ofoperation, together with further objects and advantages, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings in which:

Figure l is a central, vertical, longitudinal section through a highfrequency energy interchange device embodying one form of the presentinvention;

Figure 2 is a transverse section through the tubular body of the devicetaken on line 2-2 of Figure 1;

Figure 3 is a side elevation showing one end of the high frequencyenergy interchange device with the envelope broken away to show only theslow wave struc ture and the collector-impedance match;

Figure 4 is a central, vertical, longitudinal section taken through apart of a high frequency energy interchange device employing anotherembodiment of the present invention;

Figure 5 is a cross sectional view of the device of Figure 4 taken alongsection lines 55;

Figure 6 is a perspective view showing the impedance matching andelectron collecting member utilized in the energy interchange deviceillustrated in Figure 4;

Figure 7 is a partially broken away perspective view of still anotherenergy interchange device which employs the present invention; and

Figure 8 is a vertical longitudinal section of the embodiment of Figure7.

Referring specifically to Figure 1 of the drawing, a traveling wave tube10 is provided with a long cylindrical (circular cylinder) envelope 11which is evacuated and sealed. The envelope 11 houses an electron streamproducing electron gun 12 at one end which produces and directs a hollowcylindrical stream of electrons 13 down the length of the envelope 11.The envelope 11 also encloses a slow wave transmission line 14 which isillustrated as being a helical strip of conducting material, and anelectron collector and impedance matching member 15. The electroncollector and impedance matching member 15 is positioned at the oppositeend of the electron tube from the electron gun 12, and the slow wavetransmission line extends substantially throughout the region betweenthe extreme outer end of the collector 1-5 4 and the electron gun 12.The physical configuration and relative location of the slow wavetransmission line 14, the electron stream 13, the collecting andimpedance matching member 15, and the envelope 1]. may best be seen byan inspection of Figures 2 and 3 in connection with Figure 1.

With the arrangement just described, the electron stream 13 produced bythe electron gun 12, is directed down the length of the interactionregion in close proximity to the slow wave transmission line 14.Residual energy in the electron stream is collected on the collector andimpedance matching member 15. Thus, the electron stream 13 andelectromagnetic waves propagated down the slow wave transmission line 14interact to provide gain or amplification in the fashion typical totraveling wave tubes. That is to say that the radio frequency wavespropagated along the transmission line 14 interact with electrons in theelectron stream 13 to cause a redistribution in the form of partialbunching along the stream. As the wave and stream travel substantiallysynchronously along the helix 14, the inverse phenomenon occurs and thebunched stream induces fields and cur rents upon the helix. Theamplitude of the radio frequency waves increases along the helix becausethe electron stream gives up more energy to the helix than it abstractstherefrom. Consequently an amplification of the radio frequency waves onthe helix takes place.

Much of the traveling wave tube illustrated is shown somewhat sketchily.It is felt that more detail is not necessary since many of the elementsof the traveling wave tube are common to traveling wave tubes in generaland are not novel per se and further, the particular tube design shownis illustrated and discussed in a paper entitled A C-W UHF TWT PowerAmplifier of Extended Band Width, by Ward A. Harman, published on pages36 through 40, inclusive, of the 1957 Proceedings of the NationalConference on Aeronautical Electronics, sponsored by the Institute ofRadio Engineers, on May 13, 14 and 15, 1957, in Dayton, Ohio. Forexample, the electron gun 12 which produces the hollow electron stream13 is illustrated in block form since it is a conventional hollow streamgun known in the art as a Pierce type gun for rectilinear flow. TheHarman article supra illustrates and describes the electrode and gunconfiguration on page 39 and it is felt a detailed description of theparticular gun is not warranted. This is particularly true since anyhollow stream electron gun could be used in the particular application.Other hollow stream guns which might be used are illustrated anddescribed on pages through 163 of the book by Willis W. Harman entitledFundamentals of Electronic Motion published by the McGraw-Hill BookCompany 1953.

A series of conductive leads 16 are brought into the envelope 11 andconnected to various electrodes (not shown) of the gun 12 in order toestablish the appropriate electrode potentials to cause the formationand projection of the electron stream 13 down the axis of the device 10.Projecting tabs 17 extend outwardly from the outer periphery of the gunand rest against the inner wall 11 of the vacuum tube 10 and areprovided in order to center the gun 12 within the vacuum tube and helphold it in position The conductive leads 16 also help hold the gun 12 inposition.

In order to prevent space charge of the electrons in the stream 13 fromspreading them to such an extent that they move out of the interactionregion and intercept the slow wave circuit 14, it is necessary toprovide some focussing means. Focussing is provided by producing amagnetic field axially along the structure. This is typicallyaccomplished by providing a long annular solenoid which surrounds theentire tube. To simplify the present drawing and description, themagnetic field producing solenoid is not illustrated.

As illustrated, the helical transmission line 14 is co axiallypositioned within the glass envelope 11 by means of glass spacing rods25 which are spacedequidistant inside the glass envelope 11 in such amanner that they extend longitudinally along the wall over the regionoccupied by the helix 14. The particular main circuit or beam helix 14illustrated is designed to operate in the UHF band between approximately60 and 300 megacycles. As was previously indicated, it is not practicalto scale the circuit length from higher frequency models. For the bandof frequencies desired, a circuit length of approximately 2 feet wasfound to be practical with the thin hollow stream of electrons 13located very close to the circuit.

Radio frequency waves are introduced onto the circuit 14 by means of aconductor 18 brought in to the vacuum tube 11 at the gun end of the tubeand the amplified energy is abstracted from the beam helix by means of acoaxial cable 19 near the opposite end of the tube 11. As illustrated,the coaxial cable 19 has an outer conductor 20 connected to thecollector 15 and a central inner conductor 21 connected directly to thelast turn of the beam helix 14. The interior of the coaxial transmissionline 19 is provided with a dielectric window 24 which allows propagationof radio frequency energy down the line but provides a vacuum tightseal.

Reflections of radio frequency energy from the output end of the beamhelix must be kept to a minimum if the operation of the high frequencyenergy interchange device is to have the efiiciency desired and bestable. Therefore, the impedance of the relatively high impedance beamhelix 14 (on the order of 400 ohms) is matched to the relatively lowimpedance coaxial cable 19 (on the order of 50 ohms) using thecollectorimpedance match member 15. It is well known that matching twoimpedances of such disparate values may be accomplished by providing asection wherein the impedance varies continuously, or at least in verysmall steps, between the two extreme values. This arrangement is knownas a tapered impedance or tapered transmission line. Common taperconfigurations, that is, common ways of varying the impedance betweenthe two values to be matched with distance along the transmission line,are exponential, hyperbolic, parabolic, and cosine. These examples oftapered transmission line impedances may be found in many publications.For example, the hyperbolic line is described in Proceedings of the IRE,volume 41, No. 11, November 1953 in an article by Herbert J, Scottentitled The Hyperbolic Transmission Line as a Matching Section, page1654, the parabolic transmission line is described in an article havingthe title Parabolic Transmission Line by R. F. H. Yang in Proceedings ofthe IRE, volume 43, No. 8, August 1955 at page 1010 and the cosine linemay be found in an article by C. O. Lund entitled A Broadband TransitionFrom Coaxial Line to Helix, volume 11, No. 1 of the RCA Review, March1950 at pages 133 through 142.

The impedance matching and electron collector member 15, which is usedto match the impedance between the slow wave helical transmission line14 and the output coaxial cable 19 is substantially ogival in shape. Thecollector member is inserted within the slow wave transmission line 14in such a manner that its axis of revolution, or its central axis, iscoincident with the longitudinal axis of the helical transmission line14 and evacuated envelope 11. The external configuration of the taperedimpedance matching member is shaped so that the impedance of thetransmission line 14 varies over the matching portion in an exponentialcosine fashion as described in the Lund article supra. As previouslyindicated, the external configuration of the matching section may bevaried in any way to obtain any of the desired impedance tapersdescribed in the articles cited above. In any event, the fact that thematching member is a frustum is not crucial since the nose portion ofthe member is far enough removed from the transmission line 14 that itdoes not effect the impedance appreciably.

The impedance matching collector member 15 is held in position withinthe vacuum envelope 11 by means of a cylindrical supporting section 23which is coaxially arranged and fixed to a disk shaped annular back wallmember 22 which extends inwardly from the periphery of the back or largeend of the collector 15. The cylindrical supporting member 23 for thecollector 15 is held in the glass envelope 11 by a vacuum tight sealaround its outer periphery. Thus the entire matching member 15 is heldin position within the envelope and its interior is open to theatmosphere to provide a large cooling surface so the residual energy ofthe electron stream does not overheat the collector 15. The openinterior of collector 15 provides space for a coolant to be circulatedwithout affecting the electrical design of the device where it isnecessary to provide additional cooling.

From an inspection of Figure 1, it may be seen that the hollow electronstream 13 is collected on the front portion of the tapered impedancematching section, thus allowing most of the impedance matching to bedone beyond the point of collection of electrons from the stream. Thisarrangement eliminates the necessity of providing a separate collectorbeyond the helical slow wave transmission line 14 and a separateimpedance matching section around the helix; thus, substantially thefull length of the electron stream is available for interaction with theslow wave structure 14. As a result,

the region which must be occupied by an electron stream focussing fieldis reduced to a minimum. This means that the amount of equipmentrequired to produce this field is also reduced to a minimum, In contrastwith this arrangement, matching by conventional means is accomplishedover a region which includes both the transmission line and the electronstream. Consequently, the slow wave transmission line impedance islowered over the region where the maximum transfer of energy from theelectrons to the circuit would otherwise take place.

The arrangement illustrated allows the full impedance of the slow wavetransmission line to be maintained over nearly the entire length of theelectron stream, thus preventing possible degradation in efficiency as aresult of reducing transmission line impedance over the final outputsection of the high frequency energy interchange device.

Figures 4, 5 and 6 illustrate a portion of a high frequency energyinterchange device 30 employing another embodiment of the invention.Only the collector end of a high frequency energy interchange device 30is illustrated in this figure in order to simplify the description anddrawing.

As illustrated, the energy interchange device 30 includes a cylindricalor tubular metallic envelope 31 which is evacuated and sealed. Theenvelope 31 encloses a helical slow wave transmission line 32, anelectron collector and impedance matching member 33 which surrounds thecollector end of the slow wave transmission line 32,

and an electron stream producing electron gun (not' energy in theelectron stream is collected on the colector' member 33. Thus, theinteraction region for the device 30 is outside of the helicaltransmission line 32. However, the electron stream 34 andelectromagnetic waves propagated down the slow Wave transmission line 32interact to provide gain or amplification in the same manner describedwith respect to the device 10 of Figure The helical slow wavetransmission line .32 is wound on I a supporting dielectric cylinder 35which is also utilized to hold the helix in Position within theevacuated envelope 31. An annular groove 36, which is concentric withthe outer wall of the envelope and just large enough to hold one end ofthe dielectric helix supporting cylinder 35, is provided in the end wall37. The end of cylinder 35 is then positioned in the annular groove 36so that the helix is held coaxially within the evacuated envelope 31.The impedance matching and electron collecting member 33 is positionedcoaxially with respect to the circuit helix 32 and externally thereof sothat it collects the electrons from the stream 34 near the output end ofthe device 30. The collector matching member 33, best seen in Figures 4and 6, has a shape designed to give the desired impedance taper at theoutput end of the slow wave transmission line 32 as described inconnection with the slow wave transmission line 14 in the embodimentillustrated in Figure 1. The shape of the matching member is generallythat of the bell or horn of a trumpet. It does not necessarily fit anyshape derived from known geometrical figures; however, as illustrated,it closely represents the frustum of a hyperboloid of revolution. Theimportant point is that the open end (i.e., the end having the largestdiameter) of the matching member 33 is directed toward the electron gunend of the device 30. In other words, the end of the impedance matchingmember which is closest to the electron gun is farthest away from thetransmission line 32 so that it has the least effect upon the impedanceof the line and the end of the matching member 33 which is nearest thecollector end of the tube is very close to the transmission line 32 sothat it has the maximum effect on the impedance of the line and reducesthe impedance to some value which corresponds to the impedance of theparticular fast wave transmission line 38 which abstracts power from thedevice and for which the transmission was designed.

In the design illustrated, the impedance matching and collector member33 is held in position in the envelope 31 at both ends. The largest endof the impedance matching member 33 is held in position by the tubularenvelope 31. This is accomplished by making the outer circumference ofthe open end of the matching member 33 of such a size as to fit closelywithin the inner periphery of the cylindrical envelope 31. The smallerend of the matching member 33 is inserted in an annular groove 43 whichis concentric with the outer wall of the evacuated envelope 31. Thus,the impedance matching member is held in position within the evacuatedenvelope 31 and both ends may be brazed to the metallic wall to form aseal. If such seals are provided, a coolant may be circulated around theexternal surface of the collector member 33 without affecting operationof the device.

The particular fast wave transmission line 38 used to abstract powerfrom the device 30 is a conventional coaxial transmission line which hasan outer conductive sheath 39 and an inner conductor 40 separated by adielectric insulation 42. The coaxial transmission line is also providedwith a dielectric window 41 which acts as a seal to preventdeterioration of the vacuum within the energy interchange device 39 andto transmit electromagnetic waves abstracted from the high frequencyenergy interchange device 30.

The coaxial cable 38 is brought into the energy interchange device 30through the end wall 37 and the collector matching member 33. The outerconductive sheath 39 of the coaxial cable 38 is electrically connectedto both the envelope 31 and the collector impedance match member 33while the inner conductor 40 is connected to the helix 32. Thus, poweris abstracted from the high frequency energy interchange device 30 bythe fast wave transmission line 38.

From an inspection of Figure 4, it may be seen that the hollow electronstream 34, like the hollow stream 13 illustrated in Figure 1, iscollected on the front portion of the tapered vimpedancematchingsection, thus a lowing most of the impedance matching to be done beyondthe point of collection of electrons from the stre;m. This arrangementeliminates the necessity of providing a separate collector beyond thehelical slow wave transmission line 32 and a separate impedance matchingsection. Consequently, substantially the full length of the electronstream 34 is available for interaction with the slow wave structure 32.As a result, the region which must be occupied by an electron streamfocussing field is reduced to a minimum. This means that the amount ofequipment required to produce this field is also reduced to a minimum.In contrast with this arrangement, matching by conventional means isaccomplished over a region which includes both the transmission line andthe electron stream. Consequently, the slow wave transmission lineimpedance is lowered over the region where the maximum transfer ofenergy from the electrons to the circuit would otherwise take place.

The arrangement illustrated in Figures 4, 5 and 6 also allows the fullimpedance of the slow wave transmission line to be maintained overnearly the entire length of the electron stream, thus preventingpossible degradation in efficiency as a result of reducing transmissionline impedance over the final output section of the high frequencyenergy interchange device.

Figures 7 and 8 illustrate the invention as appplied in a linear sheetstream type high frequency energy interchange device 45. The elementsutilized in the device 45 correspond to the elements in the devicesillustrated in Figures 1 and 4 and the basic interaction mechanism ofthe apparatus disclosed in Figures 7 and 8 does not differ in anyfundamental respects. However, the construction of the elements of thedevices are somewhat different. Consequently, the impedance matching andelectron stream collecting members differ in geometrical configuration.

The device 45 includes an enclosed and evacuated envelope 46 having arectangular cross section. Envelope 45 encloses a transmission line 47of the type referred to as a zig-zag slow wave circuit, a sheet streamproducing electron gun 48 at one end, and an impedance matching andelectron-collecting member 49 at the opposite end of the device. Theelectron gun 48 pro duces and directs a sheet-like stream of electrons50 down the length of the envelope 46 beneath and in close proximity tothe zig-zag slow wave circuit 47 and the electrons are collected at theopposite end of the device on the collector and matching member 49.Thus, the electron stream 5i and the electromagnetic Waves propagateddown the zigzag slow wave circuit 47 interact to produce amplificationin a manner similar to that described with respect to the device 1% ofFigure l.

The electron gun 48 is illustrated rather diagramatically since it is aconventional gun for producing rectilinear electron flow. The gunincludes a cathode member 51 with an electron emissive surface 52, twopairs of electron focussing and directing electrodes 53 and 54,respectively, and heater elements which are not shown. Each of the pairsof electron focussing and directing electrodes 53 and 54 includes twosubstantially planar, rectangular conductive plates spaced far enoughapart to allow the rectilinear stream of electrons 50 to pass betweenthem and are sloped to insure that the electron accelerating anddirecting electric fields therebetween have the desired configuration.The design considerations for a gun of the type illustrated arediscussed in the book entitled Theory and Design of Electron Beams 2ndedition by J. R. Pierce, Van Nostrand Company, Inc., New York (1954) insection 10.1 at page 174 et seq. The particular type gun illustrated inFigures 7 and 8 is illustrated in the Pierce book in Figure 10.5 on page178. Leads are brought in through the outer end wall of the device toenergize the gun electrodes. Only two such leads are illustrated, butother leads nc ma lyn v drd t est ish ele t pds p e 9. tials. A magneticfocussing field is also provided to focus the electron stream 50. Thisis typically done by a solenoid (not shown) external to the device.

The substantially planar zig-Zag slow wave circuit 47 is suspended withits plane generally horizontal and parallel to the plane of the sheetelectron stream 50 by means of insulating supporting strips 55 whichextend down the full length of the energy interchange device 45. A pairof strips 56 is provided along each side of the device; however, it isnot convenient to illustrate both pairs of strips in either Figures 7 or8. The strips are all identical, are generally L-shaped in cross sectionand are arranged in the same general manner on opposite sides of thedevice. As may best be seen in Figure 7, the pair of slow wave circuitsupporting insulating strips 56 are arranged along one side wall of theenvelope 46 in such a manner that the legs of the Us mate to support oneedge of the slow wave circuit 47.

The particular device illustrated operates as a forward wave amplifier.As a consequence, the radio frequency energy is introduced onto the slowwave circuit 47 by means of a coaxial transmission line 57 at the gunend of the device and the amplified radio frequency energy is abstractedby means of the coaxial transmission line 58 at the collector end. Theinput coaxial transmission line 57 includes a center conductor 59 whichis connected to the input end of the slow wave transmission line and anouter conductive sheath 60 Which is brought into the energy interchangedevice and connected to an input impedance matching conductive member62. In a corresponding fashion, the output coaxial conductor 58 includesan inner conductor 61 which is connected directly to the slow wavetransmission line 47 at its output end and an outer conductive sheath 65which is connected to the output impedance matching and collector member49.

Impedance matching members 49 and 62 are of substantially identicalgeometrical configuration although, as illustrated, the size of the twomembers may differ. The portion of the members which accomplishes thematching function is the conductive surfaces 63 and 64- respectively,which are best described as having generally parabolic shapes whenviewed from the side (see Figure 8). As was the case with the impedancematching members described in connection with previous embodiments, theshape is not necessarily derived from any known geometrical figures butis designed to give the desired transition in impedance between thetransmission lines under consideration. The proper impedance match isaccomplished between the coaxial transmission line 57 at the gun end ofthe tube by positioning the matching member 62 in such a manner that itsconductive surface is near the zigzag transmission line 47 near the gunend and slopes away from the circuit. Thus, for most of the frequencyrange of interest, the impedance of the slow wave transmission line 47is low (about 50 ohms) near the gun end and is approximately that of thecoaxial transmission line 57.

Conversely, thhe conductive surface 63 of the collector impedance matchmember 49 is relatively far from the slow wave circuit 47 at the endWhere it collects electrons and is very near the slow wave circuit nearthe coaxial transmission line 58. Thus, the electron stream 50 iscollected on the front portion of the collector 49 where the collectorhas little effect on the impedance of the slow wave circuit 47.Consequently, most of the impedance matching is done beyond the point ofcollection of electrons in the stream. As a result, substantially thefull length of the stream 50 is available for interaction with the slowwave circuit 47.

Both of the matching members 49 and 62 are illustrated as solid members.This is done because it is a simple construction and such members caneasily be brazed to the walls of the envelope 46. However, the

matching members may be made hollow to provide for coolant or of anyother desired construction.

The high frequency energy interchange devices 10, 30 and 45 are allillustrated as forward wave amplifiers. It is to be particularlyunderstood that the principles set forth are equally applicable tobackward Wave ampli-t tiers and forward and backward wave oscillators.It should also be understood that the invention is equally applicable tocylindrical devices as well as the linear models illustrated.

While particular embodiments of the invention have been illustrated anddescribed, it will, of course, be understood that the invention is notlimited thereto, since many modifications both in the circuitarrangements and in the instrumentalities employed may be made. It iscontemplated that the appended claims will cover any such modificationsas fall within the true spirit and scope of the invention.

What I claim is new and desire to secure by Letters Patent of the UnitedStates is:

l. A high frequency energy interchange device including an evacuatedenvelope, a slow wave transmission line positioned within said envelope,an electron stream producing means positioned at one end of saidevacuated envelope for producing a stream of electrons in the axialdirection within said evacuated envelope and in close proximity to saidslow wave transmission line, input and output fast wave transmissionlines connected to said slow Wave transmission line to introduce radiofrequency energy thereon and abstract radio frequency energy therefromrespectively, and an impedance matching electron stream collecting meanspositioned within the end of said evacuated envelope opposite theelectron stream producing means and in the path of the electron stream,said stream collecting means having a collecting surface coextensivewith a portion of said transmission line which surface is closest tosaid transmission line at its end which is furthest removed from saidelectron stream producing means and tapers away from said transmissionline at its end which is nearest said electron gun producing means insuch a manner that the electron stream is intercepted along the lengthof the said stream collecting means whereby the impedance of said slowwave transmission line is gradually reduced and residual energy in saidelectron stream is dissipated in the region where the impedance isreduced.

2. A high frequency energy interchange device including an evacuatedenvelope, a slow wave transmission line positioned within said envelope,an electron stream producing means positioned at one end of saidevacuated envelope for producing a stream of electrons in the axialdirection Within said evacuated envelope and in close proximity to saidslow wave transmission line, input and output fast wave transmissionlines connected to said slow wave transmission line to introduce radiofrequency energy thereon and abstract radio frequency energy therefromrespectively, and an elongated impedance matching electron collectingmember positioned in the path of the electron stream near said slow wavetransmission line within the end of said envelope opposite the electronstream producing means, said impedance matching electron collectingmember extending along the length of said slow wave transmission line atleast one half circuit wave length for the lowest frequency in the bandof frequencies under consideration and having an electron collectingsurface which is farthest from said slow wave.

transmission line at its end nearest the electron stream producing meansand tapers toward said slow wave transmission line thereby to graduallyreduce the impedance of said transmission line and intercept theelectrons from said stream along its length.

3. A high frequency energy interchange device including an evacuatedenvelope, a coiled slow wave transmission line positioned within saidenvelope along the longitudinal axis thereof,

an electron stream producing means positioned at one end of saidevacuated envelope for producing a stream of electrons in the axialdirection within said evacuated envelope and said coiled slow wavetransmission line, input and output fast wave transmission linesconnected to said coiled transmission line to introduce radio frequencyenergy thereon and abstract radio frequency energy therefromrespectively, and an impedance matching electron stream collecting meanscoaxially positioned adjacent the end of said coiled slow wavetransmission line opposite the electron stream producing means, saidimpedance matching means arranged to extend over a portion of the sameregion as said transmission line and have its end which is closest tosaid electron producing means the greatest distance from saidtransmission line for performing the functions of gradually reducing theimpedance of said coiled slow wave transmission line and dissipatingresidual energy in said electron stream.

4. A high frequency energy interchange device including an evacuatedenvelope, a coiled slow wave transmission line positioned within saidenvelope along the longitudinal axis thereof, an electron streamproducing means positioned at one end of said evacuated envelope forproducing a stream of electrons in the axial direction within saidevacuated envelope and said coiled slow wave transmission line, inputand output fast wave transmission lines connected to said coiledtransmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom respectively, and an elongatedimpedance matching electron collecting member positioned within the endof said helical transmission line opposite the electron stream producingmeans and extending at least one half circuit wave length for the lowestfrequency in the band of frequencies under consideration, said impedancematching electron collecting member having an externai surface ofrevolution which has its smallest diameter nearest the electron streamproducing means.

5. A high frequency energy interchange device including an evacuatedenvelope, a coiled slow wave transmission line positioned within saidenvelope along the longitudinal axis thereof, an electron streamproducing means positioned at one end of said evacuated envelope forproducing a stream of electrons in the axial direction within saidevacuated envelope and outside said coiled slow wave transmission line,input and output fast wave transmission lines connected to said coiledtransmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom, respectively, and anelongated impedance matching electron collecting member positionedaround the end of said helical transmission line opposite the electronstream producing means and extending at least one half circuit wavelength for the lowest frequency in the band of frequencies underconsideration, said impedance matching electron collecting member havinga collecting surface of revolution which has its largest diameternearest the electron stream producing means.

6. A high frequency energy interchange device including an evacuatedenvelope, a substantially planar slow wave transmission line positionedwithin said envelope along the length thereof, an electron streamproducing means positioned at one end of said evacuated envelope forproducing a sheet stream of electrons in the axial direction within saidevacuated envelope in close proximity to said slow wave transmissionline, input and output fast wave transmission lines connected to saidslow wave transmission line to introduce radio frequency energy thereonand abstract radio frequency energy therefrom respectively, and anelongated impedance matching electron collecting member positionedadjacent the end of said slow wave transmission line opposite theelectron stream producing means in the path of the stream and extendingalong said slow wave transmission line at least one half circuit wavelength for the lowest frequency in the band of frequencies underconsideration, said impedance matching electron collecting member havingan electron collecting surface which is farthest from said slow wavetransmission line nearest the electron stream producing means and taperstoward said transmission line.

7. A high frequency energy interchange device including in combinationan evacuated envelope, a substantially planar slow wave transmissionline positioned within said envelope, an electron stream producing meansfor producing a sheet stream of electrons in the axial direction withinsaid envelope in close proximity to said slow wave transmission line,input and output fast wave transmission lines connected to said slowwave transmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom respectively, and an impedancematching electron stream collecting means positioned within the end ofsaid envelope opposite the electron stream producing means forperforming the functions of gradually reducing the impedance of saidslow wave transmission line and dissipating residual energy in saidelectron stream, said electron stream collecting means including acollecting surface coextensive with the portion of said slow wavetransmission line which surface is closest to said transmission line atits end which is furtherest removed from said electron stream producingmeans and tapers away from the transmission line at its end which isnearest said electron stream producing means.

8. In combination in a high frequency energy interchange device, anevacuated envelope, a helical slow wave transmission line coaxiallypositioned within said envelope, an electron stream producing means forproducing a hollow stream of electrons in the axial direction withinsaid helical transmission line in close proximity thereto, input andoutput fast wave transmission lines connected to said helicaltransmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom, respectively, and anelongated impedance matching electron collecting member positionedwithin the end of said transmission line opposite said electron gun,said impedance matching member having a length of at least one halfcircuit wave length for the lowest one of the band of frequencies underconsideration and having a surface of revolution which has its end withthe smallest diameter directed toward said electron gun and peripheraldimensions of such proportions that electrons from the stream arecollected adjacent a high impedance region of said slow wavetransmission line.

9. In combination in a high frequency energy interchange device, anevacuated envelope, a helical slow wave transmission line coaxiallypositioned within said envelope, an electron stream producing means forproducing a hollow stream of electrons in the axial direction withinsaid envelope in close proximity to said slow wave transmission line,input and output fast wave transmission lines connected to said helicaltransmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom respectively, and an elongatedimpedance matching electron collecting member coaxially positionedwithin the end of said envelope opposite said electron gun, saidimpedance matching member extending along the length of said slow wavetransmission line a distance of at least one half circuit wave lengthfor the lowest one of the band of frequencies under consideration andhaving a surface of revolution which has its end which is farthest awayfrom said slow wave transmission line directed toward said electron gunand peripheral dimensions of such proportions that electrons from thestream are collected adjacent a high impedance region of said slow wavetransmission line.

10. In combination in a high frequency energy interchange device, anevacuated envelope, a slow wave transmission line positioned within saidenvelope, an electron stream producing means for producing a sheetstream of electrons in the axial direction within said envelope in closeproximity to said slow wave transmission line, input and output fastwave transmission lines connected to said slow wave transmission line tointroduce radio frequency energy thereon and abstract radio frequencyenergy therefrom respectively, and an elongated impedance matchingelectron collecting member positioned adjacent the end of said slow wavetransmission line opposite said electron gun, said impedance matchingmember having a length of at least one half circuit wave length for thelowest one of the band frequencies under consideration and having asurface which varies in distance from said slow wave transmission linein such a manner that its end which is directed toward said electron gunis farth est removed from said slow wave transmission line and electronsfrom the stream are collected adjacent a high impedance region of saidslow wave transmission line.

11. In a high frequency energy interchange device of the type whichdepends upon the interaction of an electron stream produced by anelectron gun with electromagnetic waves propagated down a slow wavetransmission line adjacent the electron stream, an electron streamcollecting tapered impedance matching member located within the end ofthe device opposite the electron stream producing gun with the portionfarthest removed from the transmission line directed toward the gun andextending along the length of the transmission line.

12. A combination electron collector impedance matching member for usein a high frequency energy interchange device which depends upon theinteraction of an electron stream with electromagnetic waves propagateddown a transmission line in close proximity to the electron stream, thesaid electron collecting impedance matching member positioned adjacentthe slow wave transmission line and comprising a conductive memberhaving a tapered surface which extends at least one-half circuit wavelength along the transmission line with its end which is the greatestdistance away from the transmission line directed toward the source ofelectrons.

13. In a high frequency energy interchange device of the type whichdepends upon the interaction of an electron stream produced by anelectron gun with electromagnetic waves propagated down a helicaltransmission line surrounding the electron stream, a substantiallyogival shaped electron stream collecting impedance matching memberlocated within the end of the helical transmission line opposite theelectron stream producing gun w.th the portion having the smallestdiameter directed toward the gun.

14. A combination electron collector impedance matching member for usein a high frequency energy interchange device which depends upon theinteraction of a hollow electron stream with electromagnetic wavespropagated down a helical transmission line inside the electron stream,the said electron collecting impedance matching member comprising aconductive member having a tapered surface of revolution extending atleast one-half circuit wave length around one end of the helicaltransmission line with its largest end directed toward the source ofelectrons.

15. A high frequency energy interchange device including an evacuatedenvelope, a coiled slow wave transmission line positioned within saidenvelope along the longitudinal axis thereof, an electron streamproducing means positioned at one end of said evacuated envelope forproducing a stream of electrons in the axial direction with saidevacuated envelope and said coiled slow wave transmission line, inputand output fast wave transmission lines connected to said coiledtransmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom respectively, and an elongatedimpedance matching electron collecting member having an external surfaceof revolution which is generally ogival positioned in the end of saidhelical transmission line opposite the electron stream producing meansin such a manner that the end of reduced diameter is directed towardsaid electron stream producing means, said impedance matching memberhaving a length corresponding to at least one-half circuit wave lengthfor 14 the lowest frequency of the band of frequencies underconsideration.

16. A high frequency energy interchange device including in combinationan evacuated envelope, a helical slow wave transmission line coaxiallypositioned within said envelope, an electron stream producing means forproducing a hollow stream of electrons in the axial direction withinsaid helical transmission line in close proximity thereto, input andoutput fast wave transmission lines connected to said helicaltransmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom respectively, and asubstantially ogival shaped conductive impedance matching electronstream collecting means positioned within the end of said helical slowwave transmission line opposite the electron stream producing means forperforming the functions of gradually reducing the impedance of saidhelical slow wave transmission line and dissipating residual energy insaid electron stream.

17. In combination in a high frequency energy interchange device, anevacuated envelope, a helical slow wave transmission line coaxiallypositioned within said envelope, an electron stream producing means forproducing a hollow stream of electrons in the axial direction withinsaid helical transmission line in close proximity thereto, input andoutput fast wave transmission lines connected to said helicaltransmission line to introduce radio frequency energy thereon andabstract radio frequency energy therefrom respectively, and an elongatedimpedance matching electron collecting member having a substantiallyogival conductive surface positioned within the end of said transmissionline opposite said electron gun with its end having the smallestdiameter directed toward said electron gun, said impedance matchingmember having a length of at least one-half circuit wave length for thelowest one of the band of frequencies under consideration and peripheraldimensions of such proportions that electrons from the stream arecollected adjacent a high impedance region of said slow wavetransmission line.

18. In a high frequency energy interchange device of the type whichdepends upon the interaction of an electron stream produced by anelectron gun with electromagnetic waves propagated down a helicaltransmission line surrounding the electron stream, an electron streamcollecting impedance matching member having a shape defined by thefrustum of an ogive located within the end of the helical transmissionline opposite the electron stream producing gun with the portion havingthe smallest diameter directed toward the gun.

19. A high frequency energy interchangedevice including an evacuatedenvelope, a helical slow wave transmission line positioned coaxiallywithin said envelope, a hollow electron stream producing meanspositioned at one end of said evacuated envelope for producing a streamof electrons in the axial direction within said evacuated envelope andexternal to said slow wave transmission line, input and output fast wavetransmission lines connected to said helical transmission line tointroduce radio frequency energy thereon and abstract radio frequencyenergy therefrom respectively, and an elongated impedance matchingelectron collecting member having an internal surface of revolutionwhich is substantially defined by the frustum of a hyperboloidpositioned surrounding the end of said helical transmission lineopposite the electron stream producing means in such a manner that theend of greatest diameter is directed toward said electron streamproducing means, said impedance matching member having a lengthcorresponding to at least one-half circuit wave length for the lowestfrequency of the band of frequencies under consideration.

20. In combination in a high frequency energy interchange device, anevacuated envelope, a helical slow wave transmission line coaxiallypositioned within said enaseaeao 15 velope, an electron stream producingmeans for producing a hollow stream of electrons in the axial directionwithin said helical transmission line in close proximity thereto, inputand output fast wave transmission lines connected to said helicaltransmission line to introduce radio frequency energy thereon andabstract rad-i0 frequency energy therefrom respectively, and anelongated impedance matching electron collecting member having aconductive surface defined by the frusturn of an ogive positioned withinthe end of said transmission line 0pposite said electron gun with itsend having the smallest diameter directed toward said electron gun, saidimpedance matching member having a length of at least one-half circuitwave length for the lowest one of the band of frequencies underconsideration and peripheral dimensions of such proportions thatelectrons from the stream are collected adjacent a high impedance regionof said slow wave transmission line.

References Cited in the file of this patent UNITED STATES PATENTS (3daddition to 985,536)

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No,2,962,620 November 29, 1960 Ward A Harman It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 13, lines 22 and 23, strike out "and extending along the lengthof the transmission line" and insert the same after "gun" in line 21,same column.

Signed and sealed this 2nd day of May 1961.,

(SEAL) Attest:

ERNEST Wn SWIDER DAVID L LADD Attesting Officer Commissioner of Patents

